This invention relates to factor estimating device, method and program for estimating factor of a result that takes place in a target system under diagnosis, as well as a recording medium for recording such a factor estimating program. In particular, this invention relates to a production process management device for managing production processes of target products.
Processes for improving production steps are being required for factory production lines in order to improve the yields. In such an improvement process, steps that cause defective products are identified and apparatus are adjusted and cleaned so as to eliminate factors that cause such defective products.
In a production process including a large number of steps, however, a variety of candidates are considered as factors of causing defective products such as defective components of the production apparatus, problems involved in the setting of the production apparatus and the problems related to the routes of transportation. For example, the processes of a system for surface-mounting circuit boards may be divided into the printing, mounting and reflow steps. The printing step is where a solder paste is applied to a substrate, and the mounting step is where components are set on the substrate. In the final reflow step, heat is applied to melt the solder to attach the components. If a bridge defect occurs in such a surface-mounting system, displacement of the mask and the unclean female mold may have contributed as the cause of the defect but one or more of them may be the basic factor.
When a phenomenon that becomes a factor of a defect appears, not only does a symptom of the defect appear in the products, but there also appear some effects in the operation history of the production apparatus and the inspection history of the inspection apparatus. The amount of data related to the symptoms of these defective products and to the operation history of the production apparatus and the inspection history of the inspection apparatus becomes enormous, making it very difficult to carry out any analysis on the occurrence of the defects.
Persons in charge of production management with a lot of experience in production management may know empirically the relationship among the effects of such factors on the production and inspection apparatus and how to interpret such effects and may be able to effectively improve the production steps. Inexperienced production managers will have to examine many candidate factors one at a time to finally identify a real factor, and it turns out to be a very time-consuming effort to improve the production steps.
It is therefore being desired to provide a method of highly accurately and efficiently estimating factors of any abnormal situation independently of the level of skill of the production manager. Japanese Patent Publication Tokkai 6-196900, for example, disclosed a method of obtaining data from inspecting apparatus individually provided to each of the printing, mounting and reflow steps and making an estimate based on such data. In the case of a surface-mounting system, however, there is no guarantee that all data necessary for estimating a factor can be obtained from such inspecting apparatus. Although the area of solder as seen from the front of the substrate may be obtained by an image processing technology, for example, data on the warping of the substrate can be obtained only by a visual observation by a viewer from the side. Although a device for detecting the warping of the substrate may be considered, it is not desirable to allow the total cost of the inspecting apparatus to increase unnecessarily. In other words, it is preferable to input data from human observers in addition to data obtained from an inspection apparatus. This is to say that cooperation between an inspection apparatus and a human observer is preferable for estimating factors.
In general, knowledge data are of a network structure and a search is carried out from a root node along a path. In order to make an efficient estimate, therefore, it is necessary to optimize this network structure. This may be done, for example, by making an important item for the estimate as a node on an upstream side, but it will involve large amounts of labor and cost. In addition, so-called important items may change, depending on the circumstances of making the estimate. In summary, it is extremely difficult to form a network structure capable of efficiently making an estimate according to a variety of circumstances.